The present invention is in the field of battery technology and, more particularly, electrolyte formulations that address challenges associated with gas generation in lithium ion batteries.
Gas evolution during storage and use is a major failure mechanism of lithium ion batteries. The mechanism of gas generation is still not well understood. It has been shown that the parasitic reactions between electrolyte and electrodes could result in gaseous products. Gas formed in the cells could cause impedance growth, electrode delamination, swelling, and active material isolation. One or more of these outcomes could lead to faster capacity fade, cell failure, and safety concerns.
Lithium ion batteries operating at higher voltage are in demand to meet the comparatively higher energy density requirement for a variety of applications, including automotive applications. However, challenges in maintaining battery life over high multiples of charge/discharge cycles and safety concerns prevent higher voltage lithium ion batteries from being more widely used. For example, gas generation can in turn lead to swelling and/or deformation of the battery. In pouch type batteries (batteries with soft shells), this deformation can lead to rupture. Thus, gas generation can lead to capacity fade, power fade, and safety risks in lithium ion batteries.
Gas evolution tends to be more significant at higher operating voltages for one or more of the following reasons: (i) oxidative decomposition of solvent components, such as carbonates, leading to formation of CO2 or gaseous organic compounds; (ii) unstable cathodes at high delithiation states leading to oxygen evolution, which could cause further electrolyte decomposition; (iii) formation of acidic product from salt decomposition resulting in decomposition and reformation of the solid-electrolyte interface (SEI), which can cause rapid capacity fade and gas evolution.
Gas generation can also occur during high temperature storage of lithium ion batteries, which limits the applications in which certain lithium ion batteries can be used.
Prior efforts to reduce gas generation in lithium ion cells have focused mainly on using electrolyte additives and various approaches to electrode coating. To date, these efforts have not been successful in addressing gas evolution.
These and other challenges can be addressed by certain embodiments of the invention described herein.